Given that the current world production of zeolites amounts to around 4 million tonnes annually, a resource that shows no sign of running-out, it is of interest to predict how this market may behave , say to 2010. As I have noted "Zeolites - La Roca Magica" and "Zeolites - the Stones that Boil", these are unique materials with many highly important applications, particularly in environmental chemistry. They are hydrated aluminosilicates consisting of a negatively charged framework of micropores of molecular dimensions (usually less than 13 A in size) whose charge is balanced by sufficient positively charged cations to provide an overall electrical neutrality. In naturally occurring zeolites, the cations are mostly of the alkali and alkaline earth metals, respectively sodium and potassium and calcium and magnesium. The first mineral to be classified as a zeolite was discovered in 1756, since when about 48 natural zeolite types have been identified.
The most common natural zeolites are analcime, chabazite, clinoptilolite, heulandite (there is some speculation as to whether heulandite and clinoptilolite should simply be classified as one mineral), laumontite, phillipsite, ferrierite and erionite (which due to its fibrous nature and high iron content is a Class 1 carcinogen). Overwhelmingly, clinoptilolite is the major zeolite used for commercial applications, while chabazite and mordenite are used on a lesser scale. In an effort to exploit its extensive deposits in the United States, laumontite has come into focus as a potential commercial product. A further 150 zeolites have been artificially synthesised, the first of which was made in 1949 in the Linde division of the Union Carbide Corporation in the U.S. (Linde A, or zeolite A), and the most commercially important are zeolites A, X, Y and ZSM-5.
The natural zeolites have not gained the commercial niche-market of the synthetic forms, mainly because of limitations in availability (need to import), large variations in mineral composition (synthetic zeolites are more uniform in composition, don't need to be extracted from surrounding tuffaceous rock "tuff", clay and limestone etc), crystal size (synthetic zeolites are more uniform in this respect too, although the grains of them tend to be larger than those of their natural counterparts), porosity and pore diameter. Synthetic zeolites are generally constructed around an organic "template" which defines the above properties more precisely than nature does.
Nonetheless, natural zeolites are used on a huge scale for more low-tech applications, particularly in environmental clean-up operations, cat-litter, animal feed, fertilisers, aquaculture (fish farming), soil amendment, radioactive decontamination, industrial water softeners, heavy metal removal, heat storage, solar refrigeration and pollution control and overwhelmingly for use in light-weight cement: mostly in China, which uses 2.5 million out of the annual 4 million tonnes mined globally for this particular purpose.
The largest market for synthetic zeolite is as a water softener "builder" in detergents. As an alternative to "phosphates"which were found to cause algal blooms in lakes, around 1.3 million tonnes of zeolite A is used annually. The traditional sodium tripolyphosphate has been banned on environmental grounds, although the problem of algal bloom is not entirely eliminated since most of the "phosphate" originates from human activities, including agricultural use of "phosphate" fertilisers. With market saturation and production overcapacity in the regions of the "Industrial Triad" the potential growth market for zeolites is in the Asia-pacific region. Synthetic zeolites are also used on a large scale in the petrochemical industry for catalytic "cracking" (an inherently "green(ish)" process since it enables the production of specific product fractions from oil, specialty chemical feedstocks (e.g. para-xylene for the polyester textile industry) using less energy than would be the case without them.
There are environmental drivers to reformulate gasoline and to reduce sulphur emissions which have provided a boon to the zeolite market. The catalytic activities and selective nature of zeolites can be tuned to a considerable degree by modifying both the zeolite framework and the cations it contains. Average levels of zeolites in fluid catalytic cracking (FCC) catalysts have risen in general and ZSM-5 is now used increasingly in such catalytic composites to increase olefin (alkene) production. In terms of product selectivity, zeolites show overwhelming advantages over the more traditional Lewis Acid catalysts such as aluminium chloride and phosphoric acid based materials. Although such zeolite catalysts are used on a scale of around 117,000 tonnes annually, i.e. less than one tenth that used in detergents, the value basis is around 55% of the global market.
In the future, a greater volume is expected for the automobile industry, since by the use of zeolites in catalytic converters, the more fuel-efficient "lean burn engine" can still be used but still keeping such empowered vehicles within projected emissions targets. The lean burn engine is efficient because it runs at a higher temperature than normal and converts more of the fuel to miles on the road. However, the higher temperature also tends to "fix", combine nitrogen and oxygen , thus pumping out more NOx pollution, which the metal-loaded zeolite catalyst is able to decompose before it can escape and cause problems.
The global market for natural zeolites is expected to grow from 3.98 million tonnes to 5.5 million tonnes by 2010. In the same time period, the consumption of synthetic zeolites is projected to amount to 1.86 million tonnes. The value of the combined market would then amount to $3 billion (and that is excluding the total value of the products themselves whose production depends on zeolites).
It all looks very rosy, and one might be tempted to make extrapolative projections into the future. The only problem is that the entire zeolite industry: extraction or synthesis, and the source of chemical feedstocks for the range of industries in which they are involved (including food production using chemical fertilisers) depends on oil either at some stage or directly or both. Such economic predictions are surely only valid so long as cheap oil is available, or else a completely alternative picture might emerge. Economists and industrialists, and all of us for that matter, should not be rhetorically swept away from the imminent reality that is "Peak Oil".